In zig-zag sewing machines, a needle bar to which a needle is attached must be moved back and forth in an oscillatory movement. A machine of this type utilizes a pattern generator to produce this movement. To this end, a worm gear is mounted on the arm shaft of the machine. When the arm shaft rotates, the worm gear drives a cam-gear set with a constant angular velocity ratio. As the cam is rotated, the cam follower exhibits a back and forth motion. This motion is translated to the needle bar through known mechanisms and causes the needle bar to move in the desired manner.
The present invention is directed toward a new mechanism utilized in a pattern generator which is simplified in structure and can be manufactured at lower cost.